ISO/IEC 9,899:2011 clause 6.5--expression

6.5 Expressions

1, an expression is a sequence of operators and operands, these operators and operands specify a value calculation, or assign an object or a function, or generate side effects, or do a combination of the above operations. The order of the values of the operands of an operator is ranked before the value of the result of the operator is computed. [ Translator Note : for example,

int a = (5) * (6);

For the above expression, for the * operator, the calculation of the operands of the left and right sides of the multiplication operator is computed, and the result of the multiplication operation is computed.

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2, if the side effects on a scalar object are computed with respect to another different side effect on the same scalar object or a value using the same scalar object, the behavior is undefined if it is not pre-ordered. If an expression has more than one order of permissible sub-expressions, then the behavior is undefined if the side effect of such an order occurs in any order. [Note: The following code describes a statement expression that is not defined:

1 ; a[i+ +] = i;

The following are allowed:

1= i;

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3. The combination of the operator and the operand is specified by the syntax. [Note: The syntax specifies the precedence of an operator in an expression calculation, which is the same as the order of the main sub-clauses of the clause, and the highest priority is first introduced. Thus, for example, an expression that is allowed as a binocular operator + (6.5.6) is the expression defined in 6.5.1 to 6.5.6.  The exception is a cast expression (6.5.4) as the operand of the single-mesh operator (6.5.3) and one of the operands that follows one of the following operator pairs: the parentheses () (6.5.1) used as a combination, and the subscript brackets []  (6.5.2.1), function call parentheses () (6.5.2.2), and conditional operators ? : (6.5.15). In each main clause, the operator has the same precedence. The left or right binding is indicated in each sub-clause by the syntax used for the expression discussed in the inside. ] In addition to those specified later, the side effects and the values of the sub-expressions are not sequenced in order. [Note: In an expression, the expression is executed several times during the execution of a program, and there is no sequential order, and the calculation of its subexpression has an indeterminate sequence, and the expression does not need to be consistent in different calculations. ］

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ISO/IEC 9,899:2011 clause 6.5--expression